1. Field of the Invention
The present invention relates to an airbag apparatus for an automobile for securing safety of a passenger in an automobile such as a car when it collides, and in particular, to improvement in a vibration welding structure suitable to joining an instrument panel forming an airbag cover and reinforcement members for reinforcing an inflation unfolding section of the instrument panel and an airbag supporting frame to each other by means of vibration welding.
2. Description of the Related Art
An airbag apparatus for an automobile is available as a tool for securing safety of a passenger in a front passenger seat or a driver seat in an automobile such as a car by protecting the passenger from impact of collision when the automobile collides on its front or side.
Such a type of airbag apparatus for an automobile comprises an airbag, an airbag case to accommodate the airbag in a folded state so that the airbag can easily inflates and unfold, and an inflator that inflates the folded airbag in a short period of time. Particularly, an airbag apparatus to be used for a front passenger seat is provided inside the instrument panel, and when the speed of the automobile is suddenly reduced due to collision, the airbag apparatus operates the inflator and promptly inflates the airbag by a high-pressure gas from this inflator, whereby splitting and opening the instrument panel along a fragile splitting contour, and simultaneously, unfolding and inflating the airbag from this opening to the outside of the instrument panel to protect the passenger from an impact of collision by a cushioning action of the airbag.
Inside the instrument panel to which such an airbag apparatus for an automobile is attached, in particular, to the back surface of the instrument panel in which a fracture-opening section is formed, reinforcement members and an airbag supporting frame made of a thermoplastic resin material such as TPO (thermoplastic polyolefin) are integrally welded, whereby the fracture-opening section is prevented from being deformed into a concave shape or fractured by an impact force applied from the outside of the instrument panel, and the fracture-opening section is prevented from scattering upon separating from the instrument panel when the fracture-opening section is opened due to inflating and unfolding of the airbag. For welding such an instrument panel and the reinforcement members and the frame together, a vibration welder is used (for example, refer to U.S. Pat. No. 3,043,604).
Next, a conventional airbag apparatus for an automobile is explained with reference to FIG. 1 through FIG. 4.
FIG. 1 is a vertical sectional side view of a main portion of a conventional airbag apparatus for an automobile, FIG. 2 is a plan view taken from the arrow 2A direction in FIG. 1, FIG. 3 is a plan view of a frame and reinforcement members in the conventional airbag apparatus for an automobile, and FIG. 4 is an explanatory enlarged sectional view showing welding between an instrument panel and a frame and reinforcement members in the conventional apparatus.
As shown in FIG. 1, the airbag apparatus 1 for an automobile of the present invention comprises an instrument panel 2, an airbag 3, and airbag case 4, a frame 5, a pair of reinforcement members 6, an inflator (not shown), and so on.
The instrument panel 2 is attached to the front of a driver seat and a front passenger seat in, for example, a car, and is molded from a hard polypropylene (PP) with a thickness of 3 mm to 4 mm. On the outer surface of the instrument panel 2, a decorative surface layer (not shown) is laminated as appropriate.
On the back surface of the instrument panel 2, as shown in FIG. 1 and FIG. 2, a fragile splitting contour 7 is formed into a rectangular shape long in the horizontal direction, and on the inner side of this fragile splitting contour 7, a center splitting line 7a that divides the section surrounded by the fragile splitting contour 7 into two in the shorter length direction extends in the longer length direction. The fragile splitting contour 7 and the center splitting line 7a are for splitting and opening the section surrounded by the fragile splitting contour 7 in a biparting manner to inflate and unfold the airbag 3 to the outside of the instrument panel 2.
The fragile splitting contour 7 and the center splitting line 7a are formed by processing dot-like slit pores (blind foramen) with a depth that does not penetrate the instrument panel 2 by irradiating a laser beam of an infrared ray with a beam diameter of 0.2 to 0.5 mm and a wavelength of 10.6 μm from the back surface side of the instrument panel 2.
To the back surface of the instrument panel 2, as shown in FIG. 1, a rectangular cylindrical frame 5 molded from TPO so as to surround the rectangular fragile splitting contour 7 is vibration-welded along the fragile splitting contour 7 via an joint flange 5a provided on the frame. Inside the frame 5, attached are a pair of reinforcement members 6 made of TPO for reinforcing the section surrounded by the fragile splitting contour 7 from the back surface of the instrument panel 2.
Each reinforcement member 6 includes, as shown in FIG. 1, a support 6a for coupling the reinforcement member 6 by a dovetail groove method or the like to the inner surface of the frame 5, and a reinforcement 6c that is joined in a bendable manner to the upper end of the support 6a via a hinge 6b and vibration-welded to the back surface of the section surrounded by the fragile splitting contour 7.
The airbag 3 is accommodated in a folded state as shown in FIG. 1 in the airbag case 4 made of a metal plate member. On the side surfaces corresponding to the upper end opening 4a of the airbag case 4, a plurality of hooks 9 are provided so as to project outward. Each hook 9 engages in a hole 6e provided in the support 6a of the reinforcement member 6 and a hole 5d provided in the frame 5 corresponding to the hole 6e, whereby fixing the airbag case 4 to the frame 5.
At the lower end of the airbag case 4, an inflator accommodation section 10 for accommodating an inflator (not shown) for supplying an inflating gas into the airbag 4 is provided. The airbag case 4 is fixed to a fixing member such as a cross member 12 by a bolt and nut 13 via a supporting member 11.
Next, the welding structure of the instrument panel 2 and the frame 5 and the reinforcement members 6 in the conventional airbag apparatus for an automobile is explained with reference to FIG. 1, FIG. 3, and FIG. 4.
As shown in FIG. 1 and FIG. 3, for example, a number of convex portions 5b with a height of approximately 2 mm and a diameter or a length of approximately 3 to 5 mm are formed in an embossing manner at predetermined intervals on the entire surface of the joint flange 5a in opposition to the back surface of the instrument panel 2, and furthermore, a number of convex portions 6d like the convex portions 5b of the joint flange 5a are formed in an embossing manner at predetermined intervals on the entire surface of the reinforcement 6c in opposition to the back surface of the instrument panel 2.
The pair of reinforcement members 6 thus configured are attached to the inside of the frame 5 as shown in FIG. 1 and FIG. 3, and then the frame 5 is set together with the reinforcement members 6 at a predetermined position of a vibration welder and the instrument panel 2 is set at a predetermined position of the vibration welder, the joint flange 5a of the frame 5 and the reinforcements 6c of the reinforcement members 6 are held while pressurized to the instrument panel 2 so that the convex portions 5b of the joint flange 5a and the convex portions 6d of the reinforcements 6c are pressed against the back surface of the instrument panel 2, and in this state the joint flange 5a and the reinforcements 6c and the instrument panel 2 are relatively vibrated at an amplitude of, for example, 1.5 mm to 3.0 mm in directions of rubbing together, and by frictional heat generated on the rubbing surface, the back surface of the instrument panel 2 and the convex portions 5b and the convex portions 6d are welded to each other. Thereby, the joint flange 5a of the frame 5 and the reinforcements 6c of the reinforcement members 6 can be joined to the back surface of the instrument panel 2.
However, in the welding structure of the frame 5 and the reinforcement members 6 and the instrument panel 2 in the conventional airbag apparatus for an automobile, a number of convex portions 5b formed in an embossing manner on the joint flange 5a of the frame 5 and a number of convex portions 6d formed in an embossing manner on the reinforcements 6c of the reinforcement members 6 are pressed against the back surface of the instrument panel 2 and vibration-welded, so that such prior art has the following problem.
Namely, while pressing the convex portions 5b and 6d against the back surface of the instrument panel 2, when the joint flange 5a including the frame 5 and the reinforcements 6c including the reinforcement members 6 are vibrated at an amplitude of, for example, 1.5 mm to 3.0 mm in the arrow A direction shown in FIG. 4 with respect to the instrument panel 2 and the convex portions 5b and 6d are vibration-welded to the back surface of the instrument panel 2, the melting temperature of the convex portions 5b and 6d made of TPO is lower than that of the instrument panel 2 made of PP, so that when the tip ends of the convex portions 5b and 6d start melting due to the frictional heat, non-welded portions 5b1 and 6d1 projecting as burrs while turned up outward as shown in FIG. 4 are formed at the positions of both ends in the vibration direction (arrow A direction) of the tip ends. These non-welded portions 5b1 and 6d1 have almost no welding performance to the back surface of the instrument panel 2, and rather become factors hindering the vibration welding of the convex portions 5b and 6d. Therefore, the substantial effective welding lengths L1 of the convex portions 5b and 6d to the back surface of the instrument panel 2 become equal to or less than the projecting lengths L2 of the non-welded portions 5b1 and 6d1 (L1<L2), and the substantial welding strength of the convex portions 5b and 6d to the instrument panel 2 lowers. Therefore, to improve the welding strength of the frame 5 and the reinforcement members 6 to the instrument panel 2, it is necessary to increase the forming density of the convex portions 5b on the joint flange 5a of the frame 5 and the forming density of the convex portions 6d on the reinforcements 6c of the reinforcement members 6.
However, if the forming densities of the convex portions 5b and the convex portions 6d are increased, the pressing force to be applied to the frame 5, the reinforcement members 6, and the instrument panel 2 must be increased, thus this increasing the size of the pressurizing mechanism of the vibration welder, and causing a nonuniform pressing force for the convex portions 5b and 6d against the back surface of the instrument panel as well, thereby lowering the welding strength of the frame 5 and the reinforcement members 6 to the instrument panel back surface, and causing the portions with low welding strength to easily separate, resulting in a failure of inflating and unfolding of the airbag.
In addition, the welding areas of the embossed convex portions 5b and 6d are narrow, so that the heating value caused by the vibrating friction between the back surface of the instrument panel 2 and the convex portions 5b and 6d becomes locally large, and as a result, this heat causes local thermal deformation and discoloration on the outer surface of the instrument panel 2, and these appear as welding scars on the outer surface of the instrument panel 2. Particularly, when a decorative surface layer is provided on the surface of the instrument panel 2 of an automobile, etc., welding scars caused by thermal deformation and discoloration on the surface layer deteriorate appearance of the product and lower the quality.